An internal combustion engine generates power by burning fuel in a combustion chamber in an air media drawn into the chamber. Intake valves are operated by a camshaft in order to intake the air, and the air is drawn into the combustion chamber while the intake valves are open. In addition, exhaust valves are operated by the camshaft, and a combustion gas is exhausted from the combustion chamber while the exhaust valves are open.
The optimal operation of the intake valves and the exhaust valves depends on a rotational speed of the engine. That is, an optimal lift or optimal opening/closing timing of the valves depends on the rotational speed of the engine. In order to achieve such optimal valve operation depending on the rotational speed of the engine, various researches, such as designing of a plurality of cams and a variable valve lift (VVL) that can change valve lift according to engine speed, have been undertaken.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.